1. Field of the Invention
The present invention relates to a switching power supply unit in which an input AC voltage obtained by switching operation of an input direct current voltage is transformed by a transformer, then the transformed output AC voltage is rectified and smoothed to be outputted as an output direct current voltage.
2. Description of the Related Art
Hitherto, various types of switching power supply units have been proposed and provided for practical use. As disclosed in Japanese Laid-Open Patent Publication No. 2002-369528 and Japanese Laid-Open Patent Publication No. 2001-314080, one of them is of a type in which an input direct current voltage from a high voltage battery is switched to an input AC voltage by switching operations of a switching circuit connected to an input winding of a transformer, the obtained input AC voltage then being input into an input winding of the transformer to be converted into an output AC voltage, then the converted output AC voltage being taken out from an output winding of the transformer. The voltage appearing in the output winding in association with such switching operation of the switching circuit is then rectified by a rectifier circuit, the rectified voltage then being converted into an output direct current voltage by a smoothing circuit to be output.